When a sheet of metal is accelerated to very high speed and an obstacle is placed in its path, then because of its inertia, it would conform into or around that obstacle. Hence the sheet forms into a certain shape if the obstacle is in the form of a female die, or shears if the obstacle is a sharp edge. It is also well known that collision of a fast travelling piece of metal with another can lead to a weld, if the impact velocity and angle are in an optimum range. Collision welds are generally observed when the impact velocity is in the range of 150 m/s to 500 m/s and the impact angle is between 5 to 20 degrees. Impulse metalworking has some distinct advantages over traditional quasi-static methods. Impulse forming leads to lower spring back, higher formability and can be implemented with single sided tooling. Impact welding has been shown to result in welds which are stronger than the parent materials. It is a solid state welding process with little or no heat affected zone because of which brittle intermetallics do not form. This process is widely used for joining dissimilar metals which are very difficult, sometimes impossible, to join by traditional fusion welding processes. The two most common agents for driving the metallic workpiece to high velocities are electromagnetic forces and explosives.
The electromagnetic launch of the workpiece is based on laws of electromagnetic induction and Lorentz forces. When a conductor, considered as secondary coil, is placed in proximity to another conductor, considered as primary coil, carrying a transient current, then a current opposing the change in magnetic field is induced in the former. These conductors carrying opposite currents repel each other and hence the workpiece gets accelerated to a high velocity. The primary coil is generally insulated from the workpiece by encapsulating it in an epoxy matrix. If the cycle times are low, the joule heat developed during the process can melt the epoxy material, leading to current shortage. There are also pressure limitations on the primary coil which depend on the mechanical strength of the epoxy as well as the coil material. Hence, the application of electromagnetic forming is limited at high energies and large numbers of operations by the availability of long-lived electromagnetic coils. Besides, the workpiece either has to be electrically conductive, or it has to be driven by a conductive flyer. Use of explosives for forming or welding has problems of its own. Their safe implementation in closed industrial settings is difficult. Also, they are mostly used for only for large scale applications and there is a high expenditure on infrastructure. Besides, there are government and OSHA regulations which limit the use of explosives.